The product must be visible. Make sure that in the product list page, the "eye" (the column to the right of Price) is not red.

The product availability must be set to "This product can be purchased in my online store".Specifically, you cannot have for sale on eBay pre-order only products. The stock needs to be available and ready to ship to the buying customer.

All eBay listings need images, thus if the product doesn't have an image it will not be imported.

All eBay listings need a description.

Your Bigcommerce products are imported based on their association to categories, so make sure the product has a category defined.

If Inventory Tracking is set to "Track inventory for this product", then the quantity must be greater than zero or the product will not be imported. For products with options, if you select "Track inventory by options (from the 'Options' tab above)" then make sure at least one option has non-zero inventory.

A maximum of 3 options per product are currently supported. Products with more than 3 options are not imported, thus not listed on ebay.